Penetrating radiation examining apparatus in combination with body locating structure

ABSTRACT

Apparatus for investigating a part of a body intermediate the extremities thereof by means of X- or gamma -radiation is disclosed. The body part is surrounded by a liquid medium; the liquid medium being retained in an enclosure having a tubular inner wall formed of flexible material, and the body part is located within the inner wall. The liquid medium can be pressurised to cause the flexible inner wall to fit intimately the periphery of the body part.

United States Patent [191 Hounsfield et a1.

[451 Apr. 29, 1975 1 PENETRATING RADIATION EXAMINING APPARATUS INCOMBINATION WITI-I BODY LOCATING STRUCTURE [75] Inventors: GodfreyNewbold I-Iounsfield,

Newark; David John Gibbons, Uxbridge, both of England [73] Assignee: EMILimited, Middlesex, England [22} Filed: May 10, 1973 [21] Appl. No.:358,980

[30] Foreign Application Priority Data May 17, 1972 United Kingdom23064/72 [52] U.S. Cl. 250/360; 250/456; 250/510 [51] Int. Cl. GOln23/00 [58] Field of Search 250/358, 359, 360, 439.

[56] References Cited UNITED STATES PATENTS 3.106.640 10/1963 Oldendorf250/360 mrrsnAmns{ BISTABLES{ 3,432,657 3/1969 Slavin 250/360 3,715,5872/1973 Burkhalter et al,... 250/510 3,715.588 2/1973 Rose 250/510Primary E.\aminrWilliam F. Lindquist Attorney, Agent, or FirmFleit &Jacobson [57] ABSTRACT Apparatus for investigating a part of a bodyintermediate the extremities thereof by means of X- or y-radiation isdisclosed. The body part is surrounded by a liquid medium; the liquidmedium being retained in an enclosure having a tubular inner wall formedof flexible material, and the body part is located within the innerwall. The liquid medium can be pressurised to cause the flexible innerwall to fit intimately the periphery of the body part.

6 Claims, 6 Drawing Figures VE -CUNSTANI STARTsAT Tu JJENTEDAPRZQISYSINTEGRATURS{ BISTABLES{ SHEET 10F 2 The present invention relates toradiography and it relates especially to techniques for obtaininginformation indicative of the presence or absence of anomalies in theinterior of a body. despite the presence of other material in the body.

In the Specification of United States patent application Ser. No.212.778 now US. Pat. No. 3.773.614 there is described and claimed amethod of. and appa-' ratus for, examining a body by means of radiationsuch as X- or y-radiation. The use of the method or apparatus permitsthe calculation of the transmission or absorption coefficients ofsubstantially all elements in an at least two dimensional. notionalmatrix of elements defined in the body being examined. This is achievedby causing radiation to pass through the body along a plurality ofdiscrete paths of cross-sectional dimensions similar to those of saidelements, said paths being oriented to pass through respectivecombinations of the elements in said notional matrix. The overallabsorption of radiation along each of the discrete paths is detected andsufficient paths are used to enable the calculation of the absorption ortransmission coefficients of substantially all elements in said notionalmatrix.

The present invention is concerned with a similar arrangement. but hasthe aim of providing means for locating an elongated member, such as thehuman torso. relative to the source of radiation and the detectors.

According to the invention there is provided apparatus for examiningpart of a body by means of penetrating radiation, such as X- ory-radiation, including a source of said radiation and detector meansresponsive to said radiation located on opposite sides of the body part.the detector means being arranged to receive radiation emergent from thebody, means for orbiting the source and the detector means around thebody part, and a locating structure, transmissive of said radiation. forlocating the body part relative to the source and detector means. saidlocating structure comprising a reservoir for a liquid mediumtransmissive of said radiation, the reservoir having a flexible wall,impervious to said liquid and arranged to surround said body part makingintimate contact therewith and an outer wall arranged to orbit with saidsource and detector means around the body part and the flexible wall,the locating structure further including a rotary seal. impervious tosaid liquid, linking said outer and flexible walls to enable the outerwall to orbit around the flexible wall.

In order that the invention may be clearly understood and readilycarried into effect, the same will now be described, by way of exampleonly, with reference to the accompanying drawings, of which:

FIG. 1 illustrates. partly in a plan section and partly in blockschematic forrn, apparatus in accordance with one example of theinvention,

FIG. 2 shows a section on lines IIII of FIG. 1,

FIG. 3 illustrates waveforms explanatory of the operation of theapparatus shown in FIG. 1,

FIGS 4a and 4h show, in perspective view and crosssectional formrespectively, a calibration device suitable for use with the apparatusshown in FIG. I, and

FIG. 5 shows an alternative form of the invention.

Referring now to the drawings, and more particularly to FIGS. 1 and 2, abody 1 to be investigated is mounted in an arrangement shown generallyat 2 so that it can be illuminated by a fan-shaped swath 3 ofpenetrative radiation, such as X- or 'y-radiation, derived from a source4.

The arrangement 2, in this example, comprises an enclosure of which theouter walls 5 are formed of the material known by the Registered TradeMark Perspex" or another suitable material. The arrangement is providedwith a central aperture in which the body 1 is situated. the aperturebeing surrounded by a tubular, flexible wall 6 formed, for example. ofrubber. The enclosure between the walls 5, 6 is filled with water asindicated by the horizontal shading lines. Water can be pumped into orout of said enclosure by means of a pump 24 which is reversible in itsoperation and which communicates with said enclosure by means of a pipe23 and with a water reservoir (not shown) via a pipe 25, a closure valve25a and a removeable pipe 25h. Water is pumped out of said enclosure toallow the tubular wall 6 to expand outwardly so that the body I can beinserted therein and then water is pumped into said enclosure to causethe wall 6 to flt snugly around the part of body 1 which is to beinvestigated. In order that the body 1 and the flexible wall 6 mayremain stationary whilst the remainder of the enclosure is rotated, arotary water seal 7 is provided in the arrangement 2. The fan shapedsweep 3 passes through the arrangement 2 as shown in FIG. 2 and it willbe appreciated that the snug fit between the flexible wall 6 and thebody I must be maintained at least over the area through which the beampasses.

Having passed through the body I, the fan shaped sweep 3 is incidentupon a plurality of radially extending collimators 8 and the field ofview of each collimator defines a respective. discrete path of radiationthrough the body 1. In one example. 160 such collimators are used. Inorder that the overall degree of absorption of radiation along eachdiscrete path can be monitored, each collimator 8 communicates with arespective radiation detector 9 which may take one of several forms tobe described hereinafter.

Each detector 9 feeds a respective integrator circuit 10 and thearrangement is such that (referring toFIG. 3) each integrator receivessignals from its respective radiation detector for a given exposureperiod T At time T a negative voltage is applied in parallel to all theintegrators I0 causing them each to discharge towards zero potential.The time taken for the charge held in a given integrator to reach zeropotential will clearly be determined by the amount of charge accumulatedup to T thus if, for example a first detector accumulated chargecorresponding to a potential V and a second detector accumulated alesser amount of charge corresponding to a potential V the integratorassociated with the first detector would reach zero potential in time(Tr-T whereas the integrator associated with the second detector wouldreach Zero potential in the lesser time (T T,,). Accordingly, referringagain to FIG. 1, each integrator 10 is arranged to feed a respectivebistable circuit 11 which is such that it provides an output pulse whenthe input signal thereto reaches zero potential from a more positivepotential. The output pulses from all the circuits 11 pass on the onehand through a common OR gate 11a, and on the other hand as pathidentity signals to a store 12 associated with a computer (not shown).

An oscillator 13 is arranged to generate regularly occurring pulses at arapid rate and these are applied to an AND gate 14. The gate 14 isenabled at time T,, by the same control signal as was used to apply thenegative potential to the integrator 10, the control signal beingapplied to a terminal 15. and is arranged to pass the pulses generatedby oscillator 13 to a counter 16 continuously from the time T,, to thetime when the last of the integrators indicates zero potential.

The counter 16 is a multistage binary counter having sufficient capacityfor counting the number of pulses which would be generated by oscillator13 during the period from T,, to the maximum possible time taken for oneof the integrators to indicate zero potential, i.e.. in the ease of zeroabsorption of the radiation along a given path.

Each stage of counter 16 is connected, via a respective AND gate 17, asa decay time input to the store 12 and the gates 17 are allsimultaneously enabled when a pulse derived from any one (or more) ofthe bistable circuits 11 passes through the OR gate 11a. The store 12thus receives both path identity and decay time information and thecomputer is arranged to correlate this information to provide a figurerepresenting the absorption (or transmission) of said radiation alongeach path. These figures are then converted into logarithmic values andprocessed, for example in the manner described in the aforementionedPatent Specification, to provide a representation or a visual record ordisplay of the absorption (or transmission) coefficients ofsubstantially all the elements in a two-dimensional notional matrix ofelements defined in the body 1.

In this example, the fan shaped swath is substantially planar, but itcould alternatively be caused to have a greater thickness dimension soas to permit a three dimensional notional matrix of elements defined inthe body 1 to be investigated.

In operation. the source 4, the part of arrangement 2 outside the waterseal 7, together with the pump 24, pipes 23 and 25 and the valve 25a,from which pipe 25b is then detached, the collimators 8 and thedetectors 9 are orbited, about the centre 0 of the arrangement 2,relative to the body 1 in order to expose the body 1 to radiation from aplurality of different directions. For this purpose the aforementionedcomponents are mounted on a turntable 26 which has an aperture thereincorresponding to the diameter of the water seal 7, the turntable beingdriven by means of an electric motor 27 via a suitable drive mechanism28 which may comprise. for example, a toothed gear wheel adapted toco-operate with gear teeth provided around the periphery of theturntable 16. It is preferable in some circumstances, especially whenthe human torso is examined, that the aforementioned components berotated at a rapid rate in order that the irradiation of the torso canbe completed sufficiently rapidly that the time available for movementof internal organs of the body (which movement could cause degradationof the resolution of the apparatus) is limited. In these circumstances,it is preferable for the aforementioned components to be rotatedcontinuously rather than step wise (as described in the aforementionedPatent Specification). Because of this continuous rotation, eachexposure time effectively corresponds to the time taken for theaforementioned components to rotate through a small angle, and in orderto reduce or avoid confusion of detail produced by the relative movementbetween To evaluate zero for each detector 9 during operation of theapparatus, a shutter (not shown) may be provided between the source 4and the arrangement 2. This shutter is rotated so that it intermittentlyinterrupts the radiation during each exposure time and the zero readingobtained when the beam of radiation is interrupted is subtracted fromthe calculated absorption (or transmission) coefficient. The shutterdrive mechanism must be synchronised with the mechanism for rotating theaforementioned components of the apparatus so as to enable a zero to beevaluated during each exposure time.

It is possible. as previously mentioned, to utilise one of severalarrangements as the detectors 9 and these arrangements are set outbelow.

EXAMPLE 1 Silicon photodeteetors together with an associated wavelengthconverter phosphor, such as a Csl crystal. for converting thepenetrative radiation into optical radiation. The silicon photodeteetorscan take the form. for example. of 12-11 junction photodiodes. pinsilicon photodiodes, silicon avalanche photodiodes, silicon photofets,silicon planar junction phototransistors or silicon photo-integratedcircuits, a respective detector being provided for each collimator.

A problem which arises with photodeteetors of this kind is dark currentand the detectors require cooling to reduce this phenomenon. If however,the temperature of the array of detectors is stabilised. a higher darkcurrent can be tolerated since it is consistent and can be allowed forby suitably programming the computer.

EXAMPLE 2 Photoemissive diodes together with a wavelength converterphosphor. The diode could comprise, for example, respective separatephotodiodes for each collimator; a similar number of diodes in a commonvacuum enclosure; channel multiplier diodes; small photomultipliers orgas-filled photomultiplier photocells.

There are practical limitations on attainable sizes of photoemissivediodes, but this disadvantage can be alleviated to some extent byutilising reflecting optical systems.

EXAMPLE 3 An X- (or y-) ray sensitive vidicon. Grazing incidencereflecting optical elements made from such metals as electroless platestitanium or aluminium have made it possible to obtain good quality X-rayimages without using pinhole optics. A difficulty arises however in thatan image demagnefication of about 30:1 is required.

EXAMPLE 4 A fibre-optic vidicon fed by respective fibre optic lightguides from respective wavelength converter phosphors for eachcollimator.

EXAMPLE 5 A Digicon tube and a wavelength converter phosphor. TheDigicon is a vacuum tube containing a semitransparent photoemissivecathode of the inside of the end window, a series of accelerating andfocusing electrodes and a linear array of silicon p-n junction diodes onthe window at the other. end. A solenoidal focus field is used to directand focus electrons emitted from the photocathode. The diodes arereverse biassed and. when struck by electrons. the phenomenon ofelectron bombardment induced conductivity causes them to conduct. Theconduction current is about 2X10 or 3X10 times greater than thebombarding current and thus the tube is capable of detecting singlephotoelectrons. For this application. the Digicon requires a fibre opticend window communicating with the photocathode and fibre optic couplingbetween the Digicon and respective wavelength converter crystals foreach collimator.

EXAMPLE 6 Photographic film. A full size medical X-ray plate is movedmechanically beneath the body in a direction perpendicular to the planeof the fan-shaped beam 3. Thus a series of lines corresponding to thetransmitted radiation would be unprinted as a number of dots at eachexposure angle. After developing the lines are scanned with amicrodensitometer.

In any of the above examples. it can be advantageous, in order to avoiddead spaces between adjacent detectors. to construct the collimators sothat adjacent paths overlap to some extent. Alternatively. however. thegaps may be covered by arranging that. in a full (360 sweep around thebody. the paths not scanned on one half revolution are scanned duringthe next half revolution.

7 It is desirable. in any of the foregoing arrangements. that theindividual components of the detecting means should initially becalibrated and then re-calibrated before each new body is examinedthereby. To this end. a suitable arrangement has been found to be asfollows.

One of the individual components (such as for example the extreme lefthand collimator 8 and detector 9 shown in FIG. I) is calibratedcomprehensively by insertion of a wedge of continuously variablethickness (and hence absorbing power) between the source 4 and thecollimator 8. and the output signals fed from counter 16 to the computerare noted. Thus the computer is provided with a characteristic responsecurve for the detecting means. Of course the wedge could be insertedbetween the source 4 and all the detecting means to enable an averagecharacteristic response curve to be calculated. if desired. Once havingprovided the computer with a characteristic response curve. it is onlynecessary. during re-calibration. to provide relatively crudeinformation to the computer. for example an indication of the responsesof the detecting means to minimum and maximum amounts of radiation wouldbe sufficient. However in this example the responses of the detectingmeans under two intermediate conditions. as well under the two extremeconditions are measured. A sectoral shaped calibration member 18. madeup of four layers as shown in FIGS. 4a and 4b is used. the thinnestlayer 19 being adapted to transmit substantially all radiation incidentthereon. the next thicker layer 20 being adapted to absorb the radiationto some extent. the layer 21 being adapted to absorb the radiation to agreater extent and the thickest layer 22 being adapted to absorbsubstantially all the radiation incident thereon. In addition to. orinstead of being of different thicknesses the layers may be of differentmaterials. In operation, the calibration member 18 is lowered step-wiseinto the path of the fan-shaped swath 3. so that the amount of radiationpassed through each layer of member 18 is monitored by each detectingmeans and the output signals derived from the detecting means areprocessed as described with reference to I FIG. 1. the processterminating in a rough" recalibration curve for each component of thedetecting means being applied to the computer for comparison with thestored characteristic response curve. After the comparison has beeneffected. the computer has a store of calibration error informationwhich can be used automatically to weight the signals derived fromrespeck spex for example PVC or other suitable plastics materi-.

als could be used.

In the apparatus described with reference to FIG. I. the discharge rateof the integrators I0 is arranged to be linear. and for this reason thebinary numbers fed into the store 12 from the counter 16 have to beconverted into logarithmic values in order that the overall absorptionsuffered by radiation traversing the body along a path can be expressedas the sum of the absorptions of the elements of the matrix which aredisposed along said path.

An alternative arrangement is to cause the integrators to discharge inaccordance with a logarithmic law. When the charge held in an integratorhas decayed to a threshold level. the corresponding bistable circuit IIis arranged to feed a pulse via "OR" gate 11a to the AND gates 17. Theoperation from this point is the same as that described with referenceto FIG. 1 except. of course. that the logarithmic conversion has alreadytaken place so that it is unnecessary for the members fed into store 12from the counter 16 to be so converted.

The threshold level referred to in the last preceding paragraph can beselected to suit individual applications and if a human torso is beingexamined. the threshold may be made such that an absorption level givingrise to a charge. in an integrator. which decays to the threshold levelin a given time t is allocated a value of zero. correspondingly.absorption levels giving rise to changes which decay to the thresholdlevel in times less than I are designated positive (since greaterabsorption has occurred) whereas absorption levels giving rise tochanges which decay to'the threshold level in times greater than I aredesignated negative.

It will be appreciated that in practice it is convenient for a patent tolie supine with the required part of his torso inside the tubular.flexible wall 6. This can be achieved by arranging the apparatus withits axis of rotation horizontal and by placing suitable couches or thelike on either side of the apparatus. the couches being adapted tosupport. respectively. the upper part and the lower part of the patientsbody.

In a modification of the invention which is shown in part in FIG. 5. therotary water seal used in the apparatus shown in FIG. 1 is dispensedwith since the water enclosure is designed to remain stationary whilethe source and detectors orbit around it. In the apparatus shown in planand part cross-sectional view in FIG. 5,

a cylindrical outer wall 29 of Perspex (Registered Trade Mark) or othersuitable material is formed with annular end flanges (not shown).Extending between the inner peripheries of the two annular flanges is atubular. flexible inner wall 30 formed. for example. of rubber. TheX-ray source and detectors (not shown) are mounted on a turntable member31 which is annular and rotates around the cylindrical wall 29; the axisof rotation of the turntable being coincident with the longitudinal axisof the cylindrical wall 29. The operation of the apparatus is identicalto that of FIG. I but since the water enclosure does not rotate. theneed for the rotating water seal is avoided. Also. it is possible toprovide a permanent connection between a water pump such 24 (FIG. I) anda water reservoir. avoiding the need for a valve such as 2511 and aremoveable pipe such as 251; (FIG. 1).

Although in the foregoing description reference has been made to the useof water to surround the part of the body being examined, it is stressedthat the invention is not limited to the use of water. Other liquidmedia may be used and. in particular if the body being examined is not ahuman body. other liquids of different densities might be preferable towater. In general it is desirable to choose the liquid medium such thatits absorption to the radiation being used is similar to the averageabsorption of said radiation by the body being examined.

What we claim is:

1. Apparatus for examining part of a body by means of penetratingradiation. such as X- or 7- radiation. including a source of saidradiation and detector means responsive to said radiation located onopposite sides of the body part. the detector means being arranged toreceive radiation emergent from the body, means for orbiting the sourceand the detector means around the body part. and a locating structure.transmissive of saidradiation. for locating the body part relative tothe source and detector means. said locating structure comprising areservoir for a liquid medium transmissive of said radiation. thereservoir having a flexible wall, impervious to said liquid and arrangedto surround said body part making intimate contact therewith and anouter wall arranged to orbit with said source and detector means aroundthe body part and the flexible wall. the locating structure furtherincluding a rotary seal. impervious to said liquid. linking said outerand flexible walls to enable the outer wall to orbit around the flexiblewall.

2. Apparatus according to claim 1 wherein said flexible wall comprises asubstantially tubular flexible member having open ends whereby a bodypart intermediate the extremities of said body can be examined.

3. Apparatus according to claim 2 including means for causing said fluidto flow out of said reservoir, thereby to cause the said flexible wallto move toward said outer wall so as to permit said body part to beinserted into said locating structure. and means for causing said fluidto flow into said reservoir. thereby to cause said flexible wall to moveaway from said outer wall and to assume intimate contact with said bodypart.

4. Apparatus according to claim 2 wherein said flexible wall is formedof rubber.

5. Apparatus according to claim 2 wherein said outer wall is formed of aplastics material.

6. Apparatus according to claim 2 wherein said liquid medium is water.

1. Apparatus for examining part of a body by means of penetratingradiation, such as X- or gamma - radiation, including a source of saidradiation and detector means responsive to said radiation located onopposite sides of the body part, the detector means being arranged toreceive radiation emergent from the body, means for orbiting the sourceand the detector means around the body part, and a locating structure,transmissive of said radiation, for locating the body part relative tothe source and detector means, said locating structure comprising areservoir for a liquid medium transmissive of said radiation, thereservoir having a flexible wall, impervious to said liquid and arrangedto surround said body part making intimate contact therewith and anouter wall arranged to orbit with said source and detector means aroundthe body part and the flexible wall, the loCating structure furtherincluding a rotary seal, impervious to said liquid, linking said outerand flexible walls to enable the outer wall to orbit around the flexiblewall.
 2. Apparatus according to claim 1 wherein said flexible wallcomprises a substantially tubular flexible member having open endswhereby a body part intermediate the extremities of said body can beexamined.
 3. Apparatus according to claim 2 including means for causingsaid fluid to flow out of said reservoir, thereby to cause the saidflexible wall to move toward said outer wall so as to permit said bodypart to be inserted into said locating structure, and means for causingsaid fluid to flow into said reservoir, thereby to cause said flexiblewall to move away from said outer wall and to assume intimate contactwith said body part.
 4. Apparatus according to claim 2 wherein saidflexible wall is formed of rubber.
 5. Apparatus according to claim 2wherein said outer wall is formed of a plastics material.
 6. Apparatusaccording to claim 2 wherein said liquid medium is water.